Southern African Soap Plants and Screening of Selected Phytochemicals and Quantitative Analysis of Saponin Content

In southern Africa, several plants are used ethnobotanically as soap substitutes, however, this information resides in different literature sources. The foaming and cleansing properties of such plants are attributed mainly to the presence of saponins, but other compounds such as alkaloids and terpenoids are also implicated. This study aimed to compile a comprehensive list of plants used traditionally as soap substitutes in southern Africa and to assess the chemical properties of selected species. Qualitative phytochemical analysis was done using five solvents (ethanol, methanol, water, chloroform, and acetone) to determine the presence of saponins, alkaloids, and terpenoids in selected soap plants. Quantitative analysis of the saponin content was done employing spectrophotometric tests of methanol extracts. There are thirty-seven (37) known southern African soap plants from twenty-four (24) different families, with the Fabaceae having the highest number of species (eight). Saponin concentrations of nine previously unstudied selected soap plants are reported for the first time in this study, whereby Calodendrum capense had the highest saponin concentrations are at 107.89 ± 4.89 mg/g, followed by Noltea africana (52.65 ± 6.81 mg/g), Crinum bulbispermum (35.43 ± 4.25 mg/g), and Merwilla plumbea (25.59 ± 0.83 mg/g). The knowledge of plant composition gives a better understanding of plant chemistry and possible use of plants medicinally, industrially and as soap substitutes. Furthermore, this allows the verification and the justification of traditional plant use. Soap plants have been used traditionally for many years, the potential to commercialise the use of these plants has been realised with the increase in the use of organic products by conscious consumers hence, the purpose of this investigation can have bearing on future projects and products.